5- and 6-dialkylaminobenzylidene-aminofluorans

ABSTRACT

A NOVEL CHROMOGENIC MATERIAL OF NORMALLY COLORLESS FORM IS DISCLOSED, HAVING A STRUCTURALFORMULA:   3-(O=),2&#39;&#39;-R1,3&#39;&#39;-R,6&#39;&#39;-((R3-)2-N-),(R2-CH=N-)SPIRO(PHTHALAN-   1,9&#39;&#39;-XANTHENE)   WHEREIN R2 REPRESENTS A DIALKYLAMINOPHENYL RADICAL, R AND R1 COMPRISE HYDROGEN, HALOGEN, AND ALKYL RADICALS AND R3 REPRESENTS ALKYL RADICALS HAVING LESS THAN FIVE CARBON ATOMS-SAID MATERIALS ASSUMING A COLORED FORM UPON REACTIVE CONTACT WITH A LEWIS ACID MOLECULE. EXAMPLES INCLUDE 6&#39;&#39;-DIETHYLAMINO-5-(P-DIMETHYLAMINOBENZYLIDENE) AMINO - 2&#39;&#39;,3&#39;&#39; - DIMETHYLFLUORAN AND 2&#39;&#39;-CHLORO -6&#39;&#39;-DIETHYLAMINO - 6-(P-DIMETHYLAMINOBENZYLIDENCE)AMINO-3&#39;&#39;-METHYLFLUORAN.

Feb. 8, 1972 H UN ETAL 3,641,011

5- AND 6DIALKYLAMINOB ENZYLIDENEAMINOFLUORANS Filed Jan. 21, 1969 BASE-SHEET OF RECORD MATERIAL COATED ON THE REAR WITH MINUTE PRESSURE-RUPTURABLE CAPSULES CONTAINING LIQUID SOLUTION OF CHROMOGENIC MATERIAL DEVELOPABLE ON CONTACT WITH AN ELECTRON ACCEPTING MATERIAL OF THE LEWIS- ACID TYPE T0 COLORED FORM RECEIVING SURFACE OF UNDERSHEET COATED WITH AN ELECTRON-ACCEPTING MATERIAL OF THE LEWIS- ACID TYPE FIG. 2

INVENTORS CHAO-HAN LIN a ARTHUR J. WRIGHT BY hmx uy THEIR AGENT United States Patent @fiice 3,641,011 Patented Feb. 8, 1972 3,641,011 5- AND 6-DIALKYLAMINOBENZYLIDENE- AMINOFLUORANS Chao-Han Lin, Dayton, and Arthur J. Wright, Cincinnati, Ohio, assignors to The National Cash Register Company, Dayton, Ohio Filed Jan. 21, 1969, Ser. No. 792,277 Int. Cl. C07d 21/00 U.S. Cl. 260-240 G 5 Claims ABSTRACT OF THE DISCLOSURE A novel chromogenic material of normally Colorless form is disclosed, having a structural formula:

BACKGROUND OF THE INVENTION This invention pertains to novel chromogenic compounds for use in pressure sensitive record material and to an improved mark-forming manifold system incorporating these novel chromogenic compounds. More specific-ally, this invention pertain-s to dialkylaminophenyl-substituted dialkylamino fluoran-Schill bases which have the form of substantially colorless, i.e. white, or slightly colored solids, or approach being colorless when in liquid solution, but which may be converted to dark-colored forms upon reactive contact with appropriate acidic material.

This invention further relates to such novel chromogenic compounds wherein separate and individual chemical groups resident in the molecular structure of the novel chromogenic compounds each contribute to the final color state of the chromogenic compounds when they are reacted with a Lewis acid material. The novel chromogenic compounds of the present invention a Schiif bases derived from reaction of an aromatic aldehyde with an amine-containing, parent lactone compound. On reactive contact with a Lewis acid, the Schiff base contributes one color and the parent lactone compound contributes another colorthe optical sum of the contributions resulting in a single hue taken, in this case, to be the final color state of the novel chromogenic compound. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by effecting localized reactive contact between the novel chromogenic material and the acidic material on or in such a web or sheet, such material being brought thereto by transfer, or originally there, in situthe desired reactive contact forming dark-colored materials in the intended image areas.

:Pressure-sensitive, mark-forming systems of the prior art include that disclosed in application for Letters Patent No. 392,404, filed Aug. 27, 1964, in the names of Robert E. Miller and Paul S. Phillips, Jr. The above-mentioned patent application provides a marking system of disposing on and/ or within sheet support material, mutually reactant but unreacted mark-forming components (at least one component of which is a polymeric material) and a liquid solvent in which each of the mark-forming components is solublesaid liquid solvent being present in such form that it is maintained isolated by a pressure-rupturable barrier from at least one of the mark-forming components until an application of pressure causes a breach or rupture of the barrier in the area delineated by the pressure pattern. The mark-forming components thereby are brought into reactive contact, producing a distinctive mark.

It is an object of this invention to provide new and improved substances having chromogenic properties which may be incorporated in a web or coated onto the surface of a web to provide a novel manifolding unit, and which are, moreover, usfulvin carrying out improved methods of marking involving reactive contact with a color-activating material to yield dark-colored reaction products in areas where marking is desired.

It is another object of this invention to provide com pounds, based upon the dialkylaminophenyl-substituted dialkylamino fiuoran-Schifi bases disclosed herein which are substantially colorless, or slightly colored oifering a new and improved variety of chromogenic characteristics, and yielding novel dark-colored substances upon contact with color-activating materials.

It is a further object of this invention to provide new and improved, normally substantially colorless, chromogenic substances yielding Lewis acid-reacted color products which exhibit improved color stability on exposure to light and improved reproduction capabilities when copied by Xerographic or diazo processes.

It is a further object of this invention to provide new and improved, normally substantially colorless, chromogenic substances yielding colored reaction products when placed in reactive contact with certain selected Lewis acid materials.

It is a further object of this invention to provide a new and improved mark-forming system which comprises disposing, within a web or upon the surface of a web or sheetsupported-material, unreacted chromogenic material in a location suitable for subsequent reactive contact with an acidic material to produce dark-colored reaction products, thus providing means for making marks of desirable color intensity and hue.

In accordance with one feature of this invention, there is provided a novel, substantially colorless or slightly colored, chromogenic compound having the structural formula:

wherein R represents a dialkylaminophenyl radical, R and R comprise hydrogen, halogen, and alkyl radicals and R represents alkyl radicals having less than five carbon atoms. Examples of these novel compounds include 6' diethylamino-S-(p-dimethylaminobenzylidene)- 3 amino-2',3'-dimethylfiuoran having the structural formula:

2 chloro 6 diethylamino-6-(p-dimethylaminobenzylidene)amino-3'-methylfiuoran having structural formula:

6' diethylamino 6 (p dimethylaminobenzylidene) amino-2',3'-dimethylfiuoran having the structural formula:

and 2 chloro 6 diethylamino (p dimethylaminobenzylidene)amino 3' methylfluoran having the structural formula:

In accordance with another feature of this invention, a new composition of matter is disclosed which comprises a dark-colored product of chemical reaction having a resonant chemical structure and produced by contact of a color-activating material with one of the above-mentioned chromogenic compounds. The color-developing or activating material is an acidic substance useful for converting the chromogenic compounds to colored forms.

The method of marking of this invention, i.e., the method of developing a dark-colored material from substantially colorless or slightly colored chromogenic compounds, comprises providing a chromogenic compound selected from among the above-mentioned compounds and bringing such chromogenic compound into reactive contact with an acidic color-activating substance, in areas where marking is desired, to produce a dark-colored form of the chromogenic compound by the action thereon of said acidic substance.

Acidic materials employed in this invention can be any compound within the definition of a Lewis acid, i.e., any electron acceptor. Preferably, acidic organic polymers such as phenolic polymers are employed as the acidic material. The novel chromogenic materials exhibit the advantage of improved color stability when they are reacted with such phenolic polymers. Solution formation of solid particles of the polymeric material in a solvent system with the substantially colorless chromogenic compounds permits penetration of the dark-colored reaction product into a porous support sheet, e.g., paper, so that the colored form of the chromogenic material is absorbed into the body of the sheet and is not merely on the surface of the sheet. The absorption feature provides protection against erasure of recorded data by attrition of the surface of a record sheet made in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic representation of a two-sheet unit manifold, in perspective. The bottom surface of the overlying sheet is supplied on the surface or near the surface with a multiplicity of minute pressure-rupturable microcapsules containing a solution of the novel, substantially colorless, chromogenic component. An acidic component, such as an acid clay or a phenolic polymeric material lies within the lower web or undersheet or upon the upper surface of the lower web or undersheet. A colored mark is made by the use of a stylus, a type character, or other pressure-exerting means applied to the two-sheet unit manifold.

The encapsulated solution is released on the event of rupture of the capsules in writing operations, as is shown in FIG. 2. FIG. 2 is a sectioned view of the two-sheet unit manifold of FIG. 1. The elements are not to scale and are so-shown in order to more elfectively depict their interrelation. The released solution is transferred from the overlying or base-sheet to the receiving surface of the underlying sheet in conformance with the pressure pattern of the writing operation. The drawing shows that the top of the underlying sheet is coated or impregnated with a material reactant with the chromogenic material, e.g., an acid clay or an acidic phenolic polymer material; and that capsules are present on the overlying or base-sheet which capsules contain a liquid solution of chromogenic material. In another embodiment of the record material, however, the capsules can contain the polymeric phenolic material in liquid solution and the receiving surface of the underlying sheet can be supplied with the chromogenic material. The improvement in the system resides in the chromogenic material, which chromogenic material is the novel substance of the instant invention.

Referring again to FIG. 1, comprising an overlying or base-sheet having the chromogenic material located within or upon the sheet; it is possible to incorporate the chromogenic material in a solid, crystalline state in a binder material so that the chromogenic material may be transferred from the overlying sheet, upon the application of pressure, to deposit some of the chromogenic material on the receiving surface of the undersheet, which receiving surface carries a color-activating polymeric material. Preferably, the chromogenic substance is dissolved in an appropriate solvent and minute droplets of the solution of the chromogenic material are encapsulated in minute, rupturable, capsules. It is apparent that many other arrangements are possible, including different configurations and relationships of the solvent and all of the mark-forming materials with respect to their encapsulation and location on the supporting underlying or overlying sheets or webs can be envisioned. Such arrangements are thoroughly described in the aforementioned application Ser. No. 392,- 404 in the names of Miller et al. and need not be repeated herein.

SUMMARY OF THE INVENTION It is noted that the polymeric mark-forming components should have a common solubility with the novel chromogenic material in at least one liquid solvent when the acid-reacting material is a phenolic or other acidic organic polymer. It is also noted that in a single system several chromogenic materials may be used with the same or different polymeric materials. Several polymeric materials can be reactively contacted with a single chromogenic compound or with a mixture of chromogenic compounds.

-As mentioned above, the solvent can be maintained in physical isolation in minute droplets until such time as it is released by application of pressure. This may be accomplished by several known techniques, but, preferably, isolation is maintained by encapsulation of individual droplets of the solvent in a microcapsule according to the procedures described, for example, in U.S. Pat. No. 2,712,507, issued July 5, 1955 on the application of Barrett K. Green; 2,730,457, issued I an. 10, 1956 on the application of Barrett K. Green and Lowell Schleicher; 2,800,457, issued July 23, 1957 on the application of Barrett K. Green and Lowell Schleicher; 2,800,458, issued July 23, 1957 on the application of Barrett K. Green, reissued as Re. Pat. No. 24,899 on Nov. 29, 1960; and 3,041,289 issued June 26, 19 62 on the application of Bernard Katchan and Robert E. Miller. The microscopic capsules, when disposed within or upon a supporting web as a multiplicity in contiguous juxtaposition, are rupturable by pressure, such as normal marking pressure found, for example, in writing or typing operations.

The material or materials chosen as the wall material for the droplet-containing microcapsules, in addition to being pressure rupturable, must be inert or unreactive with respect to the intended contents of the capsules and the other mark-forming components so that the capsule wall material will remain intact under normal storage conditions until such time as it is released by an application of marking pressure. Preferred examples of eligible capsule wall materials include gelatin, gum arabic and many others thoroughly described in the aforementioned patents.

For most uses in record material, the capsule size should not exceed about 50 microns in diameter. Preferably, the capsules should be smaller than about microns in diameter.

The acidic organic polymeric material useful for developing the color of novel chromogenic compounds in this invention include phenolic polymers, phenol acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylene-maleic anhydride copolymers, carboxy polymethylene and wholly or partially hydrolyzed vinylmethylethermaleic anhydride copolymer and mixtures thereof.

More specifically, phenolic polymers found useful include alkyl-phenol acetylene resins, which are soluble in common organic solvents and possess permanent fusibility in the absence of being treated by cross-linking materials. Another specific group of useful phenolic polymers are members of the type commonly referred to as novolacs (a type of phenol-formaldehyde polymeric material) which are characterized by solubility in common organic solvents and which are, in the absence of cross-linking agents, permanently fusible. Resol resins, if they are still soluble, may be used, though they are subject to change in properties upon aging. Generally, phenolic polymer material found useful in practicing this invention is characterized by the presence of hydroxyl groups and by the absence of groups such as methylol, which tend to promote infusibility or cross-linking of the polymer, and further, by being soluble in organic solvents and relatively insoluble in aqueous media. Again, it should be remembered that mixtures of these organic polymers and other acidic materials can be employed.

A laboratory method useful in the section of suitable phenolic resins is the determination of the infrared absorption pattern. [It has been found that phenolic resins which undergo absorption in the 3200-350O cm." region (Which is indicative of hydroxyl groups) on the resin molecules and which do not absorb in the 1600-1700 cm.- region are eligible. This latter absorption region is indicative of desensitization of hydroxyl groups which desensitization renders such groups unavailable for reaction with the chromogenic materials.

The preparation of some organic polymeric materials useful for practicing this invention has been described in Industrial and Engineering Chemistry, volume 43, pages 134 to 141, January 1951, and a particular polymer thereof is described in Example 1 of US. Pat. No. 2,052,- 093, issued to Herbert Honel on Aug. 25, 1936. The preparation of the phenol-acetylene polymers has been described in Industrial and Engineering Chemistry, volume 41, pages 73 to 77, January 1949'. The preparation of maleic anhydride copolymers is described in the literature, such as, for example, one of the maleic anhydride vinyl copolymers, as disclosed in Vinyl and Related Polymers, by Calvin E. Schildknecht, Second printing, published April 1959, by John Wiley & Sons, Incorporated: See pages 65 to 68 (styrene-maleic anhydride copolymer), 530 to 531 (ethylene-maleic anhydride copolymer), and 628 to 630 (vinylmethylether-maleic anhydride copolymer).

When the acidic material used as a mark-forming component in the present invention is one of the aforementioned organic polymers, the liquid solvent chosen must be capable of dissolving it. The solvent may be volatile or nonvolatile, and a singleor multiple-component solvent may be used which is Wholly or partially volatile. Examples of volatile solvents useful in practicing the present invention include toluene, petroleum distillate, perchloroethylene, and xylene. Examples of nonvolatile solvents include high-boiling-point petroleum fractions and chlorinated biphenyls. Generally, the solvent chosen should be capable of dissolving at least about 0.3 percent, by weight, of the chromogenic material, and at least about 3 to 5 percent, by Weight, of the acidic polymeric material to yield an effective reaction. However, in the preferred system, the solvent should be capable of dissolving an excess of the polymeric material, so as to provide every opportunity for utilization of the chromogenic material and, thus, to assure maximum coloration at the reaction site.

A further criterion for selection of the solvent is that the solvent must not interfere with the mark-forming reaction. In some instances, the presence of the solvent may be found to interfere with the mark-forming reaction or diminish the intensity of the mark, in which instances the solvent chosen should be sufficiently volatile to assure its removal from the reaction site soon after having brought the mark-forming components into reactive contact so that the mark-forming reaction can proceed.

Since the mark-forming reaction requires that an intimate mixture of the components be brought about through solution of said components, one or more of the markforming components can 'be dissolved in solvent droplets isolated by encapsulation, the only requirement being that at least one of the components essential to the markforming reaction be maintained isolated until the markforming reaction is desired.

In the usual case, the mark-forming components are so chosen as to produce a mark upon application of pressure to a coated system of sheets at room temperature (20 to 25 degrees centigrade). However, the present invention also includes a system wherein the solvent component is not liquid at temperatures near room temperature but is liquid and in condition for forming solutions only at elevated temperatures.

The support sheet member on which components of the system are disposed may comprise a single or a dual sheet assembly. In the case where all components are disposed on a single sheet, the record material is referred to as a self-contained or autogenous system. Where there must be a migration of solvent, with or without the mark-forming component, from one sheet to another, the record material is referred to as a transfer system. (Such a system may also be referred to as a two-fold system, in that at least two sheets are required and each sheet includes a component, or components, essential to the mark-forming reaction.) Where an adequate amount of the colored reaction product is produced in liquid or dissolved form on a surface of one sheet, a colored mark can be recorded on a second sheet by transfer of the colored reaction product.

In a preferred case, where microcapsules are employed, they can be present in the sheet support material either disposed therethroughout or as a coating thereon, or both. The capsules can be applied to the sheet material as a dispersion in the liquid vehicle in which they were manufactured, or if desired, they can be separated from the vehicle and thereafter dispersed in a solution of the acid-reacting polymeric component (for instance, 30 grams of water and 53 grams of a 1 percent, by weight, aqueous solution of polyvinylmethylether-maleic anhydride) to form a sheet-coating composition in which, because of the inertness of the solution and the capsules, both components retain their identity and physical integrity. When this composition is disposed as a film on the support material and dried, the capsules are held therein subject to release of the contained liquid by rupture of the capsule walls. The latter technique, relying on the inertness of the microcapsule and the dispersing medium of the film-forming mark-forming polymeric component, provides a method for preparing a sensitive record material coating having the capsules interspersed directly in a dry film of the polymeric material as the film is laid down from solution. A further alternative is to disperse one or more mark-forming components, and the chromogenic-material-containing microcapsules in a liquid medium not a solvent for either the mark-forming component or the microcapsules, With the result that all components of the mark-forming system may be disposed on or within the support sheet in the one operation. Of course, the several components may be applied individually. The capsules can also be coated onto a sheet as a dispersion in a solution of polymeric material which is not necessarily reactive with the capsule-contained solution of chromogenic materials.

The respective amounts of the several components can be varied according to the nature of the materials and the architecture of the record material unit desired or required. Suitable lower amounts include, in the case of the chromogenic material, about 0.005 to 0.075 pound per ream (a ream in this application meaning five hundred (500) sheets of 25 x 38" paper, totalling 3,300 square feet); in the case of the solvent, about 1 to 3 pounds per ream; and in the case of the polymer, about 0.5 pound per ream. In all instances, the upper limit is primarily a matter of economic consideration.

The slurry of capsules can be applied to a Wet web of paper, for example, as it exists on the screen of a Fourdrinier paper machine, so as to penetrate the paper web a distance depending on the freeness of the pulp and the water content of the web at the point of application. The capsules can be placed directly in or on a paper or support sheet. Not only capsule structures, but continuous films which contain a multitude of microscopic, unencapsulated, droplets for local release in an area subjected to pressure can 'be utilized. (See for example, US. Pat. No. 2,299,694 which issued Oct. 20, 1942, on the application of Barrett K. Green.)

With respect to the acidic organic polymeric component, a solution thereof in an evaporable solvent can be introduced into an amount of water and the resulting mixture can be agitated while the evaporable solvent is blown off by an air blast. This operation leaves an aqueous colloidal dispersion slurry of the polymeric material,

which may be applied to finished paper so as to leave a surface residue, or the slurry may be applied to a wet web of paper or at the size-press station of a paper making machine. In another method for making a polymersensitized sheet, the water-insoluble polymer can be ground to a desired or required particle size in a ball mill with water, preferably with a dispersing agent, such as a small quantity of sodium silicate. If a binder material of hydrophilic properties is ground with the polymeric material, the binder itself may act as a dispersant. If desired, an amount of binder material of up to 40 percent, by weight, of the amount of polymeric material can be added to the ball-milled slurry of materialssuch binder materials being of the paper coating binder class, including, for example, gum arabic, casein, hydroxyethyl-cellulose, and latexes '(such as styrene-butadiene copolymer). If desired, oil absorbents in the form of fullers earths may be combined with the polymeric material particles to assist in retaining, in situ, the liquid droplets of chromogenic material solution to be transferred to it in data-representing configuration, for the purpose of preventing bleeding of the print.

Another method for applying the chromogenic or polymeric material individually to a single sheet of paper is by immersing a sheet of paper in 1-10 percent, by weight, solution of the material in an evaporable solvent. Of course, this operation must be conducted individually for each reactant, because if the other reactant material were present, contact of the reactants would result in a premature coloration over the sheet area. A dried sheet with one component can then be coated with a solution of another component, the solvent of which is a non-solvent to the already-supplied component.

The polymeric material can also be dissolved in ink composition vehicles to form a printing ink of colorless character and, thus, may be used to spot-print a proposed record-sheet-unit sensitized for recording, in a reactionproduced color in those spot-printed areas, by application of a solution of the chromogenic material. In the case of phenolic polymer, a printing ink may be made of up to percent, by weight, of the phenolic polymeric material in a petroleum-based solvent-the ink being built to a viscosity suitable for printing purposes. The relative amounts of reactive, mark-forming, components to be used in practice of this invention, are those most convenient and economical amounts consistent with adequate, desired or required visibility of the recorded data. The resolution of the recorded data is dependent on, among other things, particle or capsule size, distribution and amount of particles or capsules, liquid solvent migration, chemical reaction efliciency, and other factors, all of which can be optimized empirically by one skilled in the art. Such factors do not determine the principle of the present invention, which invention, in part, relates to means for enabling the bringing into solution contact, by marking pressure, two normally solid, chemically reactive, components dissolved in a common liquid solvent component held isolated as liquid droplets. The isolated liquid droplets are preferably in marking-pressure-rupturable capsules having polymeric-film walls, or are isolated, as a discontinuous phase, in a continuous marking-pressure-rupturable film.

In the color system of this invention the acidic markforming material reacts with the novel chromogenic ma terial to efiect distinctive color formation or color change. In a multi-sheet system in which an acidic organic polymer is employed, it may be desirable to include other materials to supplement the polymer reactants. For example, kaolin can be added to improve the transfer of the liquid and/or the dissolved materials between the sheets. In addition, other materials such as bentonite, attapulgite, talc, feldspar, halloysite, magnesium trisilicate, silica gel, pyrophyllite, zinc sulfate, calcium sulfate, calcium citrate, calcium phosphate, calcium fluoride, barium sulfate and tannic acid can be included.

Various methods known to the prior art and others disclosed in the aforementioned application Ser. No. 392,404

in the names of Miller et al. and in US. patent application Ser. No. 420,193 in the names of Phillips et al. can be employed in compositions useful for coating mark-forming materials into supporting sheets. An example of the compositions which can be coated onto the receiving surface of an underlying sheet of a multi-sheet to react with a capsule coating on the underside of an overlying sheet is as follows:

Having disclosed, generally, the novel chromogenic materials of this invention and preferred methods for utilizing the novel chromogenic materials, in combination with other materials, as reactive components in mark-forming record material; examples will now be disclosed wherein preparation of several of the novel chromogenic materials is described.

EXAMPLE 1 Preparation of 2'-ch1oro-6'-diethylamino-5 and/ or) 6- (p-dimethylaminobenzylidene) amino-3 '-methylfluoran (and/or) 6 amino 2' chloro-6'-diethylamino-3'- methylfluoran, a starting material in the reaction of this example, is prepared as follows: 5.0 grams of m-diethylaminophenol, 5.8 grams of 4-nitro phthalic anhydride, and 100 milliliters of benzene are refluxed together for about three hours. The mixture is cooled and extracted with about 5 percent, by weight, aqueous sodium carbonate solution and then the extract is slowly acidified to precipitate an intermediate reaction product. The precipitate obtained between pH 6 and pH 2 is collected for further use and is 2-carboxy-4'-diethylamino-2'-hydroxy-4 (and/or 5)-nitrobenzophenone. The intermediate reaction product is condensed with 4-chloro-3-methylphenl in 80 percent, by weight, sulfuric acid at about 100 degrees centigrade for about 3 hours and the reaction product is extracted with benzene, chromatographically purified over activated alumina, and recrystallized from benzene-petroleum ether to yield 2'-chloro-6'-diethylamino-3-methyl-5 (and/or 6)nitrofluoran. The nitrofluoran is reduced with stannous chloride to yield 5 (and/ or 6) amino-2'-chloro-6'-diethylamino-3'-methylfluoran, the required starting material.

To obtain the title compound of this example: 10 milligrams of the above-prepared starting material were heated with 40 milligrams of p-dimethylaminobenzaldehyde to a temperature of about 90 degrees centigrade for about 30 minutes. The reaction mixture was cooled and dissolved in about 1 milliliter of benzene. Low-boiling-point petroleum ether was used to precipitate the reaction product. The reaction product was isolated, dissolved in benzene again, and again precipitated by low-boiling-point petroleum ether. A benzene solution of the thus-purified reaction product irnparted an orange color to paper coated with a mixture of kaolin and phenolic resin.

EXAMPLE 2 Preparation of 6-diethylamino-5 (and/ or 6)-(p-dimethylaminobenzylidene) amino-2',3 -dirnethylfiuoran Preparation of the compound of this example was prepared according to the procedures and using the materials of Example 1, above, except that 3,4-dimethylphenol was substituted for 4-chloro-3-methylphenol in preparation of the starting material. The starting material for the reaction of this example was 5 (and/or 6)-amino-6'-diethylamino-2', 3-dimethy1fluoran which was reacted with pdimethylaminobenzaldehyde, as in Example 1, to yield the aminofluoran compound of this example. A benzene solution of the purified reaction product imparted an orange color to paper coated with a mixture of kaolin and phenolic polymer.

What is claimed is:

1. A chromogenic compound having the structural formula:

wherein R represents a dialkylaminophenyl radical wherein the alkyl group has less than five carbon atoms, and wherein R and R represent at least one chemical radical selected from the group consisting of hydrogen, halogen, and alkyl radicals having less than five carbon atoms; and

R represents a chemical radical selected from the group consisting of hydrogen and alkyl radicals having less than five carbon atoms.

2. The chromogenic compound of claim 1 wherein R is a p-dimethylaminophenyl radical, R is a methyl radical, R is a chloro radical and R is an ethyl radical, said compound being 2-chloro-6'-diethylamino-5-(p-dimethylaminob enzylidene amino-3'-methylfluoran.

3. The chromogenic compound of claim 1 wherein R is a p-dimethylaminophenyl radical, R is a methyl radical, and R is a chloro radical, and R is an ethyl radical, said compound being 2-chloro-6-diethylamino-6-(p-dimethylaminob enzylidene) amino-3'-methylfiuoran.

4. The chromogenic compound of claim 1 wherein R is a p-dimethylaminophenyl radical, R and R are methyl radicals and R is an ethyl radical, said compound being 6' diethylamino-S-(p-dimethylaminobenzylidene)amino- 2',3-dimethylfluoran.

5. The chromogenic compound of claim 1 wherein R is a p-dimethylaminophenyl radical, R and R are methyl radicals and R is an ethyl radical, said compound being 6 diethylamino-6-(p-dimethylaminobenzylidene)amino- 2,3'-dimethylfiuoran.

References Cited FOREIGN PATENTS 1,507,389 11/1967 France 260335 HENRY R. J ILES, Primary Examiner G. T. TODD, Assistant Examiner US. Cl. X.R. 

